[BUG linux-next] KASAN bug is raised on linux-next-20160414 with huge tmpfs on

[Shi, Yang]

Hi folks,

When I run the below test on my ARM64 machine with NFS mounted rootfs, I 
got KASAN bug report. The test runs well if mnt is not mounted with 
"huge=1".

# mount -t tmpfs -o huge=1 tmpfs /mnt
# cp -a /opt/ltp /mnt/

BUG: KASAN: use-after-free in nfs_readdir+0x2c4/0x848 at addr 
ffff80000b7f4000
Read of size 4 by task crond/446
page:ffff7bffc02dfd00 count:2 mapcount:0 mapping:ffff80001c2cae98 index:0x0
flags: 0x6c(referenced|uptodate|lru|active)
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff80002402da80
CPU: 0 PID: 446 Comm: crond Tainted: G        W 
4.6.0-rc3-next-20160414-WR8.0.0.0_standard+ #13
Hardware name: Freescale Layerscape 2085a RDB Board (DT)
Call trace:
[<ffff20000820bc90>] dump_backtrace+0x0/0x2b8
[<ffff20000820bf6c>] show_stack+0x24/0x30
[<ffff200008a28928>] dump_stack+0xb0/0xe8
[<ffff2000084c2cf0>] kasan_report_error+0x518/0x5c0
[<ffff2000084c32c0>] kasan_report+0x60/0x70
[<ffff2000084c1854>] __asan_load4+0x64/0x80
[<ffff20000868e1dc>] nfs_readdir+0x2c4/0x848
[<ffff2000085189d8>] iterate_dir+0x120/0x1d8
[<ffff2000085190dc>] SyS_getdents64+0xdc/0x170
[<ffff200008204ee0>] __sys_trace_return+0x0/0x4
Memory state around the buggy address:
 ffff80000b7f3f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff80000b7f3f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff80000b7f4000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff80000b7f4080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff80000b7f4100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

BUG: KASAN: use-after-free in nfs_do_filldir+0x88/0x298 at addr 
ffff80000b7f4000
Read of size 4 by task crond/446
page:ffff7bffc02dfd00 count:2 mapcount:0 mapping:ffff80001c2cae98 index:0x0
flags: 0x6c(referenced|uptodate|lru|active)
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff80002402da80
CPU: 0 PID: 446 Comm: crond Tainted: G    B   W 
4.6.0-rc3-next-20160414-WR8.0.0.0_standard+ #13
Hardware name: Freescale Layerscape 2085a RDB Board (DT)
Call trace:
[<ffff20000820bc90>] dump_backtrace+0x0/0x2b8
[<ffff20000820bf6c>] show_stack+0x24/0x30
[<ffff200008a28928>] dump_stack+0xb0/0xe8
[<ffff2000084c2cf0>] kasan_report_error+0x518/0x5c0
[<ffff2000084c32c0>] kasan_report+0x60/0x70
[<ffff2000084c1854>] __asan_load4+0x64/0x80
[<ffff20000868cb98>] nfs_do_filldir+0x88/0x298
[<ffff20000868e3a0>] nfs_readdir+0x488/0x848
[<ffff2000085189d8>] iterate_dir+0x120/0x1d8
[<ffff2000085190dc>] SyS_getdents64+0xdc/0x170
[<ffff200008204ee0>] __sys_trace_return+0x0/0x4
Memory state around the buggy address:
 ffff80000b7f3f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff80000b7f3f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff80000b7f4000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff80000b7f4080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff80000b7f4100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

Thanks,
Yang